Rubber composition for high-load transmission belt and high-load transmission belt from the rubber composition

ABSTRACT

This invention has an object of enhancing the cold resistance of a heavy duty power transmission V-belt without impairing its durability at high temperatures, ensuring its sufficient power transmission capability and concurrently enhancing its permanent set resistance. To attain the object, the invention employs, for a rubber element of the belt, a rubber composition in which 20 to 40 parts by weight of a metal salt monomer of an organic acid and 5 to 35 parts by weight of short fibers are mixed into 100 parts by weight of a rubber component composed of EPDM and HNBR in their ratio of 55/45 to 75/25, the rubber hardness measured with a durometer Type D is 40 to 60, the value of t 5  given by a Gehman torsion test is −50° C. to −35° C., and the amount of acetone extract from the rubber component is 9% or less.

TECHNICAL FIELD

This invention relates to rubber compositions for heavy duty powertransmission belts and heavy duty power transmission belts using thesame.

BACKGROUND ART

Known variable speed V-belts for automotive four-wheel vehicles,motorcycles and the like include a single cogged V-belt with cogs on thebelt inner face only, a double cogged V-belt with cogs on both the beltinner and back faces, and a hybrid V-belt in which a plurality of blocksare engaged at specified pitches and intervals in the belt lengthwisedirection with bilaterally paired tension members. For heavy duty powertransmission V-belts, lateral pressures from pulleys are high.Therefore, in order to withstand such high lateral pressures, rubbercompositions used for the above various kinds of variable speed heavyduty power transmission belts are required to have a high elasticmodulus after crosslinked. In addition, these rubber compositions aftercrosslinked are also required to have excellent heat aging resistanceand flex fatigue cracking resistance and exhibit a small permanent setdue to temperature and pressure.

To meet these requirements, use has conventionally been made ofperoxide-crosslinked hydrogenated acrylonitrile butadiene rubbersreinforced with a metal salt monomer of an unsaturated carboxylic acid,typically, such as zinc dimethacrylate or zinc diacrylate. For suchhydrogenated acrylonitrile butadiene rubbers (HNBR), as the content ofmetal salt monomer is increased, their elastic modulus becomes higherand therefore they become more advantageous to heavy duty powertransmission. However, on the other side of the coin, the HNBRsdeteriorate their heat aging resistance and flex fatigue crackingresistance, thereby tending to increase permanent set. To cope withthis, a technique has conventionally been employed which determines anoptimal amount of the unsaturated metal salt monomer mixed into a rubbercomposition for a belt in consideration of the balance between beltpower transmission capability required according to the particularapplication, and required heat resistance, cracking resistance and lowpermanent deformability.

Meanwhile, there has been increasing demand in recent years fordevelopment of power transmission belts which can satisfy not only theforegoing characteristic requirements but also their durabilityrequirement even when used in cold climates such as North America andNorth Europe, or in other words, globally serviceable power transmissionbelts.

If the above-mentioned HNBR-based rubber compositions are used to meet,for example, flexibility and softness requirement at −35° C., a largeamount of plasticizer such as oil needs to be mixed thereinto. Then, theresultant rubbers would have adverse effects of decreased elasticmodulus and increased permanent set on belts using the rubbers, and inturn the belts would be difficult to preserve the above good balanceamong the foregoing characteristics.

On the other hand, attention has in recent years been given, as rubbermaterials for power transmission belts having both heat resistance andcold resistance, to ethylene-α-olefin elastomers such asethylene-propylene copolymer (EPM), ethylene-propylene-diene terpolymer(EPDM) or ethylene-octene copolymer.

For ethylene-α-olefin elastomer-based rubber compositions, however, theresultant rubbers have a low elastic modulus. It may be possible toenhance the elastic modulus of such rubber by increasing the amount offiller such as carbon black. In that case, however, there arise aproblem that a belt using the rubber exhibits an extremely largeself-heating when bent and has a poor cracking resistance, thereby notreaching a practical level. To solve this problem, it has beenconsidered to enhance the rubber elastic modulus by adding a metal saltmonomer of an unsaturated carboxylic acid to the ethylene-α-olefinelastomer.

For example, Japanese Unexamined Patent Publication (Kokai) No. 5-17635describes a belt rubber composition in which 100 parts by weight of anethylene-α-olefin elastomer having a Mooney viscosity (ML₁₊₄, 100° C.)of 10 to 70 and containing 75 mol % or more of ethylene units is mixedwith 15 to 80 parts by weight of a metal salt monomer of anethylene-unsaturated carboxylic acid and 0.2 to 10 parts by weight of anorganic peroxide.

International Patent Publication Number WO97/22662 describes a beltrubber composition in which 100 parts by weight of an ethylene-α-olefinelastomer having an ethylene content of 40 to 70 wt % is mixed with 32to 100 parts by weight of a metal salt of an unsaturated carboxylicacid.

Japanese Unexamined Patent Publication (Kohyo) No. 9-500930 and itscorresponding U.S. Pat. No. 5,610,217 describe belt rubber compositionsin which 100 parts by weight of an ethylene-α-olefin elastomer is mixedwith 1 to 30 parts by weight of a metal salt of an α-β-unsaturatedorganic acid and 250 parts by weight or less of a reinforcing filler.These documents also describe a technique that up to 25 parts by weightof HNBR is blended into 100 parts by weight of the ethylene-α-olefinelastomer.

International Patent Publication Number WO97/22663 describes a beltrubber composition in which a basic rubber blend composed of 41 to 49parts by weight of an ethylene-α-olefin elastomer and 51 to 59 parts byweight of HNBR is mixed with 5 to 80.5 parts by weight of a metal saltof an unsaturated carboxylic acid.

However, in the case of adding a metal salt monomer of an unsaturatedcarboxylic acid to an ethylene-α-olefin elastomer, the resultant rubberhas a high elastic modulus but extremely deteriorates its crackingresistance. The above-described Japanese Unexamined Patent Publication(Kokai) No. 5-17635 mentions that a rubber composition in which anethylene-α-olefin elastomer having an ethylene content of about 70 mol %or less is mixed with a metal salt monomer of an unsaturated carboxylicacid would not provide high strength, and presumes that this is due topoor dispersibility of the metal salt monomer. The above-describedproblem of deteriorated cracking resistance is presumably also due topoor dispersibility of the metal salt monomer. In the above case ofusing the ethylene-α-olefin elastomer containing 75 mol % or more ofethylene units, the resultant rubber achieves a high strength, butcauses crystallization at low temperatures because of its high ethylenecontent. Therefore, it does not go far enough to satisfy the flexresistance of a belt at low temperatures.

The above technique of blending an ethylene-α-olefin elastomer and HNBRmay be effective in enhancing the cold resistance of the resultantrubber. However, since the content of ethylene-α-olefin elastomer is assmall as 41 to 49 parts by weight in 100 parts by weight of the entirerubber component, this does not have a sufficient effect of enhancingthe rubber cold resistance. On the other hand, if the amount of oilmixed is increased in order to improve the cold resistance, this easilycauses a permanent deformation (permanent set) of the rubber.

Furthermore, in the above case of a blending ratio of 25 parts by weightor less of HNBR to 100 parts by weight of ethylene-α-olefin elastomer,its high blending ratio of ethylene-α-olefin elastomer increases thecold resistance but deteriorates the cracking resistance, which isdisadvantageous to durability at high temperatures.

The present invention is directed to the fabrication of a heavy dutypower transmission belt such as a variable speed belt using a rubbercomposition obtained by blending ethylene-α-olefin elastomer and HNBR,and has an object of achieving a good balance among high elasticmodulus, heat aging resistance, cracking resistance, permanent setresistance and cold resistance.

Furthermore, the present invention has another object of enhancing thecold resistance of the belt without impairing its durability at hightemperatures, ensuring its sufficient power transmission capability andconcurrently enhancing its permanent set resistance.

DISCLOSURE OF INVENTION

In the present invention, a suitable amount of metal salt monomer isadded into a rubber composition of HNBR and ethylene-α-olefin elastomerwith their blending ratio at a suitable value, thereby enhancing thecold resistance of the resultant belt without impairing its durabilityat high temperatures, and ensuring its sufficient power transmissioncapability. Furthermore, the cold resistance improvement effect ofethylene-α-olefin elastomer is used to reduce the amount of plasticizeradded such as oil, thereby improving permanent set resistance.

To be more specific, one aspect of the present invention is directed toa rubber composition for a heavy duty power transmission belt which hasa rubber hardness of 40 to 60 when measured with a durometer Type D, avalue of t₅ of −50° C. to −35° C. when given by a Gehman torsion test,and an amount of acetone extract of 9% or less, wherein:

(a) 20 to 40 parts by weight of a metal salt monomer of an organic acidis mixed into 100 parts by weight of a rubber component composed of anethylene-α-olefin elastomer and hydrogenated acrylonitrile butadienerubber;

(b) 5 to 35 parts by weight of short fibers are mixed into 100 parts byweight of the rubber component; and

(c) the amount of the ethylene-α-olefin elastomer in 100 parts by weightof the rubber component is 55 to 75 parts by weight.

Since the amount of the ethylene-α-olefin elastomer is 55 to 75 parts byweight in 100 parts by weight of a rubber component composed of theethylene-α-olefin elastomer and hydrogenated acrylonitrile butadienerubber, this is advantageous in ensuring the cold resistance of the beltwithout impairing its durability at high temperatures. In this context,if the amount of the ethylene-α-olefin elastomer is less than 55 partsby weight, this does not have a sufficient effect of enhancing the coldresistance. On the other hand, if the amount of the ethylene-α-olefinelastomer exceeds 75 parts by weight, the cold resistance is improvedbut the cracking resistance is deteriorated. This is disadvantageous interms of the ensuring of the durability at high temperatures. The amountof the ethylene-α-olefin elastomer more preferably ranges from 60 to 70parts by weight.

Furthermore, since the mixing ratio of the metal salt monomer of theorganic acid is 20 to 40 parts by weight, the hydrogenated acrylonitrilebutadiene rubber can be reinforced. This increases the elastic modulus,and in other words, increases the rubber hardness to enhance the heavyduty power transmission capability of the belt. In this context, if themixing ratio of the metal salt monomer of the organic acid is less than20 parts by weight, this does not have a sufficient effect of the rubberreinforcement. On the other hand, if the mixing ratio of the metal saltmonomer of the organic acid exceeds 40 parts by weight, this improvesthe elastic modulus but is disadvantages in terms of the crackingresistance. The mixing ratio of the metal salt monomer of the organicacid more preferably ranges from 25 to 30 parts by weight.

Furthermore, as described above, the amount of the ethylene-α-olefinelastomer is 55 to 75 parts by weight per 100 parts by weight of therubber component, thereby improving the cold resistance. Therefore, theamount of plasticizer mixed such as oil can be reduced, and in turn theamount of oil mixed can be reduced to zero, which is advantageous inenhancing the permanent set resistance of the belt. The amount ofacetone extract of 9% or less is aimed at reducing the amount ofplasticizer mixed such as oil to enhance the permanent set resistance.The amount of acetone extract is more preferably 6% or less.Furthermore, in mixing the oil, its mixing ratio is preferably 5 partsby weight or less per 100 parts by weight of the rubber component.

The mixing of short fibers is aimed at increasing the rubber hardnesswhile suppressing rubber self-heating at belt bending, thereby improvingthe belt power transmission capability. More specifically, a belt isrepeatedly bent during travels around pulleys. If the matrix rubberconstituting the belt (rubber component except for short fibers) isincreased in hardness for the purpose of enhancing the belt powertransmission capability, then the rubber increases the amount of heatproduced at belt bending to be prone to thermal degradation. Therefore,the rubber hardness is increased by the mixing of short fibers, whilethe amount of heat produced by the rubber at belt bending is suppressedto a low level.

In the above case, if the mixing ratio of short fibers is less than 5parts by weight, a sufficient effect of the rubber reinforcement cannotbe achieved. Therefore, there arises a need to increase the hardness ofthe matrix rubber, which is disadvantageous in suppressing the heatproduction of the rubber. On the other hand, if the mixing ratio ofshort fibers exceeds 35 parts by weight, their dispersibility in therubber is degraded, resulting in deteriorated physical properties ofrubber for a power transmission belt.

The short fibers preferably comprise organic short fibers with a tensilemodulus of 15 GPa to 300 GPa, and 5 to 20 parts by weight of the organicshort fibers are preferably mixed into the rubber component. Morespecifically, if the tensile modulus is less than 15 GPa, the rubberreinforcement effect is low. This creates a need to enhance the hardnessof the matrix rubber or increase the mixing ratio of short fibers, whichleads to the above problem of heat production or poor dispersibility.The tensile modulus ranges preferably from 15 GPa to 100 GPa, or morepreferably from 60 GPa to 100 GPa.

The present invention preferably employs, as the ethylene-α-olefinelastomer, ethylene-propylene copolymer (EPM), ethylene-propylene-dieneterpolymer (EPDM) or ethylene-octene copolymer.

The bound acrylonitrile content in the hydrogenated acrylonitrilebutadiene rubber may be approximately 40%. However, a boundacrylonitrile content of 20% or less can achieve both the coldresistance and permanent set resistance of the belt even when the amountof the ethylene-α-olefin elastomer is small.

The present invention can employ, as the metal salt monomer of theorganic acid, a metal salt of an unsaturated monocarboxylic acid such asacrylic acid, methacrylic acid, crotonic acid or 3-butenoic acid, ametal salt of an unsaturated dicarboxylic acid such as maleic acid,fumaric acid or itaconic acid, or a metal salt of an unsaturateddicarboxylic acid monoester such as monomethyl maleate, monoethylmaleate or monoethyl itaconate. The metal used is not particularlylimited so long as it forms a salt with an ethylene-unsaturatedcarboxylic acid, but appropriate metals include zinc, magnesium, calciumand aluminium. The use of zinc diacrylate or zinc dimethacrylate isparticularly preferable.

The organic fibers used in the present invention includepoly(paraphenylene-terephthalamide) fibers,co-poly(paraphenylene-3,4′-oxydiphenylene-terephthalamide) fibers,poly(metaphenylene-isophthalamide) fibers,poly(paraphenylene-benzobisoxazole) fibers, polyvinyl alcohol fibers,and holaromatic polyester fibers. The organic fibers used may be eitherof a single type or a blend of two or more types.

In compounding the above constituents, the metal salt monomer of theorganic acid and the hydrogenated acrylonitrile butadiene rubber arepreferably premixed to sufficiently disperse the metal salt monomer ofthe organic acid in the hydrogenated acrylonitrile butadiene rubber, andthe hydrogenated acrylonitrile butadiene rubber containing the dispersedmetal salt monomer of the organic acid, the ethylene-α-olefin elastomerand the short fibers are preferably mixed into a compound. This enhancesthe dispersibility of the metal salt monomer of the organic acid toensure the reinforcement of the hydrogenated acrylonitrile butadienerubber, which is advantageous in improving the cracking resistance.

Furthermore, if necessary, in order to enhance the compatibility betweenethylene-α-olefin elastomer and hydrogenated acrylonitrile butadienerubber, polar groups such as carboxyl groups can be introduced into oneor both of the polymers.

The rubber composition for a heavy duty power transmission beltpreferably has a rubber hardness of 40 to 60 when measured with adurometer Type D, and a value of t₅ of −50° C. to −35° C. when measuredby a Gehman torsion test.

The rubber hardness preference of 40 or more is because the belt canthereby attain good power transmission capability under heavy dutyconditions. In order to enhance such power transmission capability,higher rubber hardness is more preferable. However, if the rubberhardness exceeds 60, the belt extremely deteriorates its crackingresistance and thus extremely shortens the life from a high-temperaturedurability test. Therefore, the rubber hardness is preferably not morethan 60. More preferably, the rubber hardness ranges from 45 to 58.

The t₅ preference of −35° C. or less in a Gehman torsion test is becausethe belt can thereby attain the low-temperature durability (coldresistance). In order to obtain an excellent low-temperature durability,t₅ is preferably −37° C. or less.

Another aspect of the present invention is a rubber composition for aheavy duty power transmission belt, wherein a metal salt monomer of anorganic acid and short fibers are mixed into a rubber component composedof an ethylene-α-olefin elastomer and hydrogenated acrylonitrilebutadiene rubber, the rubber hardness measured with a durometer Type Dis 40 to 60, the value of t₅ given by a Gehman torsion test is −50° C.to −35° C., and the amount of acetone extract from the rubber componentis not more than 9% or not more than 6%.

Therefore, this aspect of the present invention can achieve a goodbalance among high elastic modulus, heat aging resistance, crackingresistance, permanent set resistance and cold resistance, andparticularly enhance the cold resistance of the belt without impairingits high-temperature durability, ensure its sufficient powertransmission capability and concurrently enhance its permanent setresistance.

The rubber compositions described so far are applicable to a coggedV-belt in which a large number of cogs are formed at specified pitcheson the belt inner face only or on both the belt inner and back faces.More specifically, the rubber compositions are applicable to at leastone of rubber elements constituting the cogged V-belt, for example, acompression rubber which is the rubber element closer to the belt innerface than the tension member, a tension rubber which is the rubberelement closer to the belt back face, both of the tension andcompression rubbers, or an adhesion rubber for holding the tensionmember at a proper position.

These applications can achieve a good balance among high elasticmodulus, heat aging resistance, cracking resistance, permanent setresistance and cold resistance, and particularly enhance the coldresistance of the belt without impairing its high-temperaturedurability, ensure its sufficient power transmission capability andconcurrently enhance its permanent set resistance, which is advantageousin enhancing the belt durability.

Furthermore, the above rubber compositions are applicable to a heavyduty power transmission V-belt comprising: a tension member formed of arubber layer having a cord embedded thereinto; and a plurality of blocksengaged at specified pitches and intervals in the lengthwise directionof the belt with the tension member, and specifically to the rubberlayer of the heavy duty power transmission V-belt. This application canachieve a good balance among high elastic modulus, heat agingresistance, cracking resistance, permanent set resistance and coldresistance, and particularly enhance the cold resistance of the beltwithout impairing its high-temperature durability, ensure its sufficientpower transmission capability and concurrently enhance its permanent setresistance, which is advantageous in enhancing the belt durability.

As described so far, according to the rubber composition of the presentinvention, rubber constituting a belt can achieve a good balance amonghigh elastic modulus, heat aging resistance, cracking resistance,permanent set resistance and cold resistance, which is advantageous inenhancing the belt durability.

Furthermore, since the cogged V-belt or the heavy duty powertransmission V-belt with a large number of blocks engaged with a tensionmember according to the present invention employs the rubber compositionfor a rubber element of the belt, the rubber element can achieve a goodbalance among high elastic modulus, heat aging resistance, crackingresistance, permanent set resistance and cold resistance, which isadvantageous in enhancing the belt durability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of part of a cogged V-belt according to thepresenting invention.

FIG. 2 is a side view of the above cogged V-belt.

FIG. 3 is a perspective view of part of a hybrid V-belt according to thepresenting invention.

FIG. 4 is an enlarged cross-sectional view taken along the line II—II ofFIG. 3.

FIG. 5 is an enlarged side view of a block of the above hybrid V-belt.

FIG. 6 is an enlarged side view of a tension member of the above hybridV-belt.

FIG. 7 is a graph showing the relationships between the rubberhardnesses of cogged V-belts and their transmitted torques.

FIG. 8 is a graph showing the relationships between the rubberhardnesses of hybrid V-belts and their transmitted torques.

FIG. 9 is a graph showing the relationships between the rubberhardnesses and high-temperature durable lives of cogged V-belts.

FIG. 10 is a graph showing the relationships between the rubberhardnesses and high-temperature durable lives of hybrid V-belts.

FIG. 11 is a graph showing the relationships between the Gehman torsionlevels t₅ and cold durable cycles of cogged V-belts.

FIG. 12 is a graph showing the relationships between the Gehman torsionlevels t₅ and cold durable cycles of hybrid V-belts.

FIG. 13 is a graph showing the relationships between the amounts ofacetone extract and center distance variations of cogged V-belts.

FIG. 14 is a graph showing the relationships between the amounts ofacetone extract and post-travel interferences of hybrid V-belts.

FIG. 15 is a graph showing the relationship between the mixing ratio ofzinc dimethacrylate and rubber hardness.

FIG. 16 is a graph showing the relationship between the amount ofacetone extract and the mixing ratio of oil.

FIG. 17 is a graph showing the relationship between the amount of oiland Gehman torsion level t₅.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

<Heavy Duty Power Transmission Belt Construction>

Cogged V-Belt

As shown in FIGS. 1 and 2, a cogged V-belt 10 comprises a tension rubberlayer 1 at the back face, a compression rubber layer 2 at the innerface, an adhesion rubber layer 3 interposed between the tension andcompression rubber layers 1 and 2, and a cord 4 embedded in the adhesionrubber layer 3. The surface of the tension rubber layer 1 is providedwith a large number of cogs 5 at specified pitches in the beltlengthwise direction to have a corrugated shape. The surface of thecompression rubber layer 2 is also provided with a large number of cogs6 at specified pitches in the belt lengthwise direction to have acorrugated shape. Further, the surface of the compression rubber layer 2is covered with a bottom fabric 7. The cord 4 is placed spirally in theadhesion rubber layer 3 with its turns extending in the belt lengthwisedirection and aligned at specified pitches in the belt widthwisedirection.

Para-aramid fibers Kevlar® produced by DuPont are used for the cord 4. Anylon fabric is used as the bottom fabric 7. A rubber compositionaccording to the present invention is used for the tension andcompression rubber layers 1 and 2. The rubber layers 1 and 2 containshort fibers oriented in the belt widthwise direction.

Heavy Duty Power Transmission Hybrid V-Belt

As shown in FIG. 3, this V-belt 20 is constituted by bilaterally pairedendless tension members 30 and 30, and a large number of blocks 40, 40,. . . engaged at specified intervals in the belt lengthwise directionwith the tension members 30 and 30.

Each tension member 30 is designed as an integral structure consistingof: a rubber layer 31; a cord 32 placed spirally in the rubber 31 withits turns extending in the belt lengthwise direction and aligned atspecified pitches in the belt widthwise direction; and top and bottomfabrics 35 and 36 covering the top and bottom faces of the rubber layer31. The top face of each tension member 30 is formed with groove-likeupper recesses 33, 33, . . . extending in the belt widthwise directionand at specified pitches in correspondence with the blocks 40. Thebottom face of each tension member 30 is formed with lower recesses 34,34, . . . extending in the belt widthwise direction and at specifiedpitches in correspondence with the upper recesses 33, 33, . . .

The cord 32 is formed from a twisted yarn or plait made of highstrength, high elastic modulus aramid fibers and subjected to dippinginto an RFL liquid and rubber cement and drying.

The top and bottom fabrics 35 and 36 are formed of an aramid wovenfabric that is processed to have stretchability in the belt lengthwisedirection and rubberized.

Each block 40 has fitting slots 41 and 41 formed in the right and leftsides for detachably receiving the corresponding tension members 30 fromsideways. Further, each block 40 also has contact parts 42, 42 forcontacting a groove surface of a pulley on its side surfaces locatedabove and below each fitting slot 41. The tension members 30 and 30 arefitted into the fitting slots 41 and 41 of each block 40, respectively.

On the upper wall surface of each fitting slot 41 of each block 40, anupper ridge 43 is formed which extends in the belt widthwise directionand is mated with the corresponding upper recess 33 in the top face ofthe tension member 30. On the lower wall surface of each fitting slot41, a lower ridge 44 is formed which extends in the belt widthwisedirection and is mated with the corresponding lower recess 34 in thebottom face of the tension member 30. Through the mating engagement ofthe upper and lower ridges 43 and 44 of each block 40 with the upper andlower recesses 33 and 34 of the tension member 30, the blocks 40, 40, .. . are securely engaged with the tension members 30 and 30 so as not tobe wobbled in the belt lengthwise direction.

Each block 40 is formed from a hard, thermosetting phenol resin materialmixed with short aramid fibers, milled carbon fibers or the like. Insidethe block 40, as shown in FIGS. 4 and 5, a high strength, high elasticmodulus reinforcing member 45 made of a lightweight aluminum alloy orother like material is embedded substantially in the thicknesswisemiddle of the block 40.

The reinforcing member 45 consists of upper and lower beams 45 a and 45b extending in the widthwise (transverse) direction and a center pillar45 c vertically connecting between laterally middle portions of both thebeams 45 a and 45 b, and is thereby formed in substantially H-shape.

Furthermore, the distance t2 in the tension member 30 as shown in FIG.6, i.e., the distance between the bottom surface of the upper recess 33(more specifically, the top surface of the upper fabric 35) and thebottom surface of the corresponding lower recess 34 (more specifically,the bottom surface of the lower fabric 36), is previously set slightly,for example, about 0.03 to 0.15 mm larger than the distance t1 in eachblock 40 as shown in FIG. 4, i.e., the distance between the lower end ofthe upper ridge 43 and the upper end of the lower ridge 44 (t2>t1).Under this setting, in assembling individual blocks 40 onto the tensionmember 30, the tension member 30 is incorporated into each block 40while thicknesswise compacted by the block 40.

As shown in FIG. 4, the lateral side surface 30 a of the tension memberprojects slightly (for example, 0.03 to 0.15 mm) beyond the resin-madecontact parts 42, 42 of each block 40 outward in the belt widthwisedirection (a projection allowance Δd). The lateral side surface 30 a ofthe tension member contact the pulley groove surface together with thecontact parts 42 on the side surface of the block 40, so that the block40 and the tension member 30 take up their shares of lateral pressurefrom the pulley. Thus, shocks at the entry of each block 40 into thepulley groove are eased by the lateral side surface 30 a of the tensionmember 30.

A rubber composition according to the present invention is used for therubber layer 31. The rubber layer 31 includes short fibers oriented inthe belt widthwise direction.

<Rubber Composition>

Table 1 shows the specification of ingredients of a rubber compositionused for the rubber layers 1 and 2 of the above cogged V-belt and therubber layer 31 of the tension member 30 of the above hybrid V-belt.

TABLE 1 Ingredients Makers Trade names EPDM JSR EP24 EPM JSR EP11Ethylene-octene copolymer DuPont Dow Engage 8180 Elastomers Japan HNBR 1Zeon Corporation Zetpol 2010 HNBR 2 Zeon Corporation Zetpol 4110 Zincdimethacrylate Kawaguchi Chemical Actor ZMA Zinc diacrylate AsadaChemical zinc diacrylate powder Antioxidant Ouchi Shinko Chemical Nocrac224 Zinc oxide Sakai Chemical zinc oxide Type 3 Silica Tokuyama TokusilU-15 Oil 1 Asahi Denka ADK CIZER RS107 Oil 2 Idemitsu Kosan PW-90Peroxide Nippon Oil & Fats Perximon F40 Short nylon fibers Asahi KaseiNylon 66, type T-5 Short co-poly(paraphenylene-3,4′-oxydiphenylene-Teijin Technora terephthalamide) fibers Shortpoly(paraphenylene-terephthalamide) fibers DuPont Kevlar 29 Shortpoly(metaphenylene-isophthalamide) fibers Teijin Conex HT Shortpoly(paraphenylene-benzobisoxazole) fibers Toyobo Zylon-HM Shortpolyvinyl alcohol fibers Kuraray Kuralon 5501 Short holaromaticpolyester fibers Kuraray Vectran HT

Tables 2-1 to 2-16 and Tables 3-1 and 3-2 show the results obtained byexamining physical properties of a rubber composition and its effects onresultant cogged and hybrid V-belts by changing the formulation of itsingredients. In the rows of “Ingredients” in the following tables, thevalues are given in parts by weight.

TABLE 2-1 Formulation No. 1 2 3 4 5 6 7 8 Ingredients EPDM 25 25 25 2525 25 25 25 HNBR 1 75 75 75 75 75 75 75 75 Zinc oxide 10 10 10 10 10 1010 10 Antioxidant 1 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 20 Oil 110 10 10 10 10 15 15 15 Oil 2 0 0 0 0 0 0 0 0 Peroxide 7 7 7 7 7 7 7 7Zinc 10 20 30 40 50 10 20 30 dimethacrylate Short nylon fibers 10 10 1010 10 10 10 10 Short Technora 10 10 10 10 10 10 10 10 fibers RubberRubber hardness 35 41 44 53 68 33 37 42 properties Gehman torsion T₅−30.8 −30.7 −30.3 −30.0 −29.8 −33.6 −33.2 −33.0 (° C.) Amount of acetone8.7 8.4 8.1 7.8 7.5 11.2 10.8 10.4 extract (%) Permanent set (%) 32.339.2 46.2 53.1 60.0 34.2 41.1 48.1 Cogged Center distance 2.5 2.3 2.2V-belt variation (%) Transmitted torque 122 134 136 139 148 (Nm)High-temp. 170 158 152 131 51 durable life (hrs) Low-temp. durable 11 108 life (cycles) Hybrid Post-travel −0.22 −0.22 −0.21 V-belt interference(mm) Transmitted torque 380 430 435 446 476 (Nm) High-temp. 495 478 471436 149 durable life (hrs) Low-temp. durable 15 13 10 life (cycles) 

TABLE 2-2 Formulation No. 9 10 11 12 13 14 15 Ingredients EPDM 25 25 2525 25 25 25 HNBR 1 75 75 75 75 75 75 75 Zinc oxide 10 10 10 10 10 10 10Antioxidant 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 Oil 1 15 15 20 2020 20 20 Oil 2 0 0 0 0 0 0 0 Peroxide 7 7 7 7 7 7 7 Zinc dimethacrylate40 50 10 20 30 40 50 Short nylon fibers 10 10 10 10 10 10 10 ShortTechnora 10 10 10 10 10 10 10 fibers Rubber Rubber hardness 53 64 31 3742 50 61 properties Gehman torsion T₅ −32.8 −32.4 −36.4 −36.1 −35.8−35.5 −34.9 (° C.) Amount of acetone 10.0 9.7 13.7 13.1 12.6 12.1 11.7extract (%) Permanent set (%) 55.0 61.9 36.1 43.0 49.9 56.9 63.8 CoggedCenter distance V-belt variation (%) Transmitted torque (Nm) High-temp.durable life (hrs) Low-temp. durable life (cycles) Hybrid Post-travelV-belt interference (mm) Transmitted torque (Nm) High-temp. durable life(hrs) Low-temp. durable life (cycles) 

TABLE 2-3 Formulation No. 16 17 18 19 20 21 22 23 Ingredients EPDM 35 3535 35 35 35 35 35 HNBR 1 65 65 65 65 65 65 65 65 Zinc oxide 10 10 10 1010 10 10 10 Antioxidant 1 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 20Oil 1 10 10 10 10 10 15 15 15 Oil 2 0 0 0 0 0 0 0 0 Peroxide 7 7 7 7 7 77 7 Zinc 10 20 30 40 50 10 20 30 dimethacrylate Short nylon fibers 10 1010 10 10 10 10 10 Short Technora 10 10 10 10 10 10 10 10 fibers RubberRubber hardness 34 40 44 54 67 32 37 42 properties Gehman torsion T₅−32.5 −32.1 −31.8 −31.6 −31.1 −35.3 −35.0 −34.8 (° C.) Amount of acetone8.7 8.4 8.1 7.8 7.5 11.2 10.8 10.4 extract (%) Permanent set (%) 32.339.2 46.2 53.1 60.0 34.2 41.1 48.1 Cogged Center distance 2.4 2.4 2.3V-belt variation (%) Transmitted torque 122 134 135 140 147 (Nm)High-temp. 176 162 158 138 59 durable life (hrs) Low-temp. durable 20 1815 life (cycles) Hybrid Post-travel −0.25 −0.23 −0.23 V-beltinterference (mm) Transmitted torque 380 432 436 446 476 (Nm) High-temp.513 502 483 446 158 durable life (hrs) Low-temp. durable 25 22 20 life(cycles) 

TABLE 2-4 Formulation No. 24 25 26 27 28 29 30 Ingredients EPDM 35 35 3535 35 35 35 HNBR 1 65 65 65 65 65 65 65 Zinc oxide 10 10 10 10 10 10 10Antioxidant 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 Oil 1 15 15 20 2020 20 20 Oil 2 0 0 0 0 0 0 0 Peroxide 7 7 7 7 7 7 7 Zinc 40 50 10 20 3040 50 dimethacrylate Short nylon fibers 10 10 10 10 10 10 10 ShortTechnora 10 10 10 10 10 10 10 fibers Rubber Rubber hardness 54 61 31 3641 49 61 properties Gehman torsion T₅ −34.6 −34.4 −38.1 −37.5 −37.3−37.1 −36.5 (° C.) Amount of acetone 10.0 9.7 13.7 13.1 12.6 12.1 11.7extract (%) Permanent set (%) 55.0 61.9 36.1 43.0 49.9 56.9 63.8 CoggedCenter distance V-belt variation (%) Transmitted torque (Nm) High-temp.durable life (hrs) Low-temp. durable life (cycles) Hybrid Post-travelV-belt interference (mm) Transmitted torque (Nm) High-temp. durable life(hrs) Low-temp. durable life (cycles) 

TABLE 2-5 Formulation No. 31 32 33 34 35 36 37 38 Ingredients EPDM 45 4545 45 45 45 45 45 HNBR 1 55 55 55 55 55 55 55 55 Zinc oxide 10 10 10 1010 10 10 10 Antioxidant 1 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 20Oil 1 10 10 10 10 10 15 15 15 Oil 2 0 0 0 0 0 0 0 0 Peroxide 7 7 7 7 7 77 7 Zinc 10 20 30 40 50 10 20 30 dimethacrylate Short nylon fibers 10 1010 10 10 10 10 10 Short Technora 10 10 10 10 10 10 10 10 fibers RubberRubber hardness 35 41 45 53 68 33 37 42 properties Gehman torsion T₅−34.2 −34.1 −33.7 −33.4 −33.2 −37.0 −36.6 −36.4 (° C.) Amount of acetone8.7 8.4 8.1 7.8 7.5 11.2 10.8 10.4 extract (%) Permanent set (%) 32.339.2 46.2 53.1 60.0 34.2 41.1 48.1 Cogged Center distance 2.5 2.4 2.4V-belt variation (%) Transmitted torque 120 134 136 139 148 (Nm)High-temp. 175 162 154 135 53 durable life (hrs) Low-temp. durable 35 3228 life (cycles) Hybrid Post-travel −0.26 −0.25 −0.24 V-beltinterference (mm) Transmitted torque 380 432 436 446 475 (Nm) High-temp.501 489 473 443 155 durable life (hrs) Low-temp. durable 46 44 40 life(cycles) 

TABLE 2-6 Formulation No. 39 40 41 42 43 44 45 Ingredients EPDM 45 45 4545 45 45 45 HNBR 1 55 55 55 55 55 55 55 Zinc oxide 10 10 10 10 10 10 10Antioxidant 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 Oil 1 15 15 20 2020 20 20 Oil 2 0 0 0 0 0 0 0 Peroxide 7 7 7 7 7 7 7 Zinc 40 50 10 20 3040 50 dimethacrylate Short nylon fibers 10 10 10 10 10 10 10 ShortTechnora 10 10 10 10 10 10 10 fibers Rubber Rubber hardness 55 63 31 3642 50 62 properties Gehman torsion T₅ −36.2 −35.8 −39.8 −39.5 −39.2−38.9 −38.3 (° C.) Amount of acetone 10.0 9.7 13.7 13.1 12.6 12.1 11.7extract (%) Permanent set (%) 55.0 61.9 36.1 43.0 49.9 56.9 63.8 CoggedCenter distance V-belt variation (%) Transmitted torque (Nm) High-temp.durable life (hrs) Low-temp. durable life (cycles) Hybrid Post-travelV-belt interference (mm) Transmitted torque (Nm) High-temp. durable life(hrs) Low-temp. durable life (cycles) 

TABLE 2-7 Formulation No. 46 47 48 49 50 51 52 53 Ingredients EPDM 55 5555 55 55 55 55 55 HNBR 1 45 45 45 45 45 45 45 45 Zinc oxide 10 10 10 1010 10 10 10 Antioxidant 1 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 20Oil 1 10 10 10 10 10 15 15 15 Oil 2 0 0 0 0 0 0 0 0 Peroxide 7 7 7 7 7 77 7 Zinc 10 20 30 40 50 10 20 30 dimethacrylate Short nylon fibers 10 1010 10 10 10 10 10 Short Technora 10 10 10 10 10 10 10 10 fibers RubberRubber hardness 34 40 45 55 67 32 37 42 properties Gehman torsion T₅−36.0 −35.6 −35.3 −35.1 −34.6 −38.7 −38.4 −38.2 (° C.) Amount of acetone8.7 8.4 8.1 7.8 7.5 11.2 10.8 10.4 extract (%) Permanent set (%) 32.339.2 46.2 53.1 60.0 34.2 41.1 48.1 Cogged Center distance 2.5 2.5 2.33.5 V-belt variation (%) Transmitted torque 121 134 137 141 148 (Nm)High-temp. 165 153 139 131 50 durable life (hrs) Low-temp. durable 65 6360 ≧100 life (cycles) Hybrid Post-travel −0.25 −0.24 −0.23 −0.35 V-beltinterference (mm) Transmitted torque 385 432 435 449 470 (Nm) High-temp.481 465 452 435 135 durable life (hrs) Low-temp. durable 81 80 78 ≧100life (cycles) 

TABLE 2-8 Formulation No. 54 55 56 57 58 59 60 Ingredients EPDM 55 55 5555 55 55 55 HNBR 1 45 45 45 45 45 45 45 Zinc oxide 10 10 10 10 10 10 10Antioxidant 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 Oil 1 15 15 20 2020 20 20 Oil 2 0 0 0 0 0 0 0 Peroxide 7 7 7 7 7 7 7 Zinc 40 50 10 20 3040 50 dimethacrylate Short nylon fibers 10 10 10 10 10 10 10 ShortTechnora 10 10 10 10 10 10 10 fibers Rubber Rubber hardness 53 61 32 3742 49 61 properties Gehman torsion T₅ −38.0 −37.8 −41.5 −40.9 −40.7−40.5 −39.9 (° C.) Amount of acetone 10.0 9.7 13.7 13.1 12.6 12.1 11.7extract (%) Permanent set (%) 55.0 61.9 36.1 43.0 49.9 56.9 63.8 CoggedCenter distance 3.4 4.1 3.9 V-belt variation (%) Transmitted torque (Nm)High-temp. durable life (hrs) Low-temp. durable ≧100 ≧100 ≧100 life(cycles) Hybrid Post-travel −0.33 −0.39 −0.37 V-belt interference (mm)Transmitted torque (Nm) High-temp. durable life (hrs) Low-temp. durablelife ≧100 ≧100 ≧100 (cycles) 

TABLE 2-9 Formulation No. 61 62 63 64 65 66 67 68 Ingredients EPDM 65 6565 65 65 65 65 65 HNBR 1 35 35 35 35 35 35 35 35 Zinc oxide 10 10 10 1010 10 10 10 Antioxidant 1 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 20Oil 1 5 5 5 5 5 10 10 10 Oil 2 0 0 0 0 0 0 0 0 Peroxide 7 7 7 7 7 7 7 7Zinc 10 20 30 40 50 10 20 30 dimethacrylate Short nylon fibers 10 10 1010 10 10 10 10 Short Technora 10 10 10 10 10 10 10 10 fibers RubberRubber hardness 35 41 47 57 70 33 40 45 properties Gehman torsion T₅−35.9 −35.5 −35.3 −35.1 −34.7 −37.7 −37.4 −37.1 (° C.) Amount of acetone6.0 5.8 5.6 5.5 5.3 8.7 8.4 8.1 extract (%) Permanent set (%) 30.4 37.344.3 51.2 58.1 32.3 39.2 46.2 Cogged Center distance 1.9 1.8 1.6 2.4 2.3V-belt variation (%) Transmitted torque 119 134 137 142 151 (Nm)High-temp. 150 141 130 124 39 durable life (hrs) Low-temp. durable 55 5351 ≧100 ≧100 life (cycles) Hybrid Post-travel −0.15 −0.14 −0.14 −0.25−0.24 V-belt interference (mm) Transmitted torque 390 432 439 458 482(Nm) High-temp. 451 432 406 380 130 durable life (hrs) Low-temp. durable75 73 72 ≧100 ≧100 life (cycles) 

TABLE 2-10 Formulation No. 69 70 71 72 73 74 75 Ingredients EPDM 65 6565 65 65 65 65 HNBR 1 35 35 35 35 35 35 35 Zinc oxide 10 10 10 10 10 1010 Antioxidant 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 Oil 1 10 10 1515 15 15 15 Oil 2 0 0 0 0 0 0 0 Peroxide 7 7 7 7 7 7 7 Zinc 40 50 10 2030 40 50 dimethacrylate Short nylon fibers 10 10 10 10 10 10 10 ShortTechnora 10 10 10 10 10 10 10 fibers Rubber Rubber hardness 53 64 32 3541 49 62 properties Gehman torsion T₅ −36.8 −36.2 −40.4 −40.1 −39.8−39.5 −38.9 (° C.) Amount of acetone 7.8 7.5 11.2 10.8 10.4 10.0 9.7extract (%) Permanent set (%) 53.1 60.0 34.2 41.1 48.1 55.0 61.9 CoggedCenter distance 2.2 3.4 3.3 V-belt variation (%) Transmitted torque (Nm)High-temp. durable life (hrs) Low-temp. durable ≧100 ≧100 ≧100 life(cycles) Hybrid Post-travel −0.22 −0.32 −0.31 V-belt interference (mm)Transmitted torque (Nm) High-temp. durable life (hrs) Low-temp. durable≧100 ≧100 ≧100 life (cycles) 

TABLE 2-11 Formulation No. 76 77 78 79 80 81 82 83 Ingredients EPDM 7575 75 75 75 75 75 75 HNBR 1 25 25 25 25 25 25 25 25 Zinc oxide 10 10 1010 10 10 10 10 Antioxidant 1 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 2020 Oil 1 5 5 5 5 5 10 10 10 Oil 2 0 0 0 0 0 0 0 0 Peroxide 7 7 7 7 7 7 77 Zinc 10 20 30 40 50 10 20 30 dimethacrylate Short nylon fibers 10 1010 10 10 10 10 10 Short Technora 10 10 10 10 10 10 10 10 fibers RubberRubber hardness 35 41 45 58 69 34 40 42 properties Gehman torsion T₅−36.6 −36.2 −35.9 −35.7 −35.2 −39.4 −39.1 −38.9 (° C.) Amount of acetone6.0 5.8 5.6 5.5 5.3 8.7 8.4 8.1 extract (%) Permanent set (%) 30.4 37.344.3 51.2 58.1 32.3 39.2 46.2 Cogged Center distance 1.9 1.8 1.8 2.6 2.5V-belt variation (%) Transmitted torque 121 133 134 141 148 (Nm)High-temp. 140 131 127 116 39 durable life (hrs) Low-temp. durable 71 7068 ≧100 ≧100 life (cycles) Hybrid Post-travel −0.14 −0.13 −0.12 −0.26−0.24 V-belt interference (mm) Transmitted torque 389 431 435 457 479(Nm) High-temp. 400 393 375 356 145 durable life (hrs) Low-temp. durable89 87 85 ≧100 ≧100 life (cycles) 

TABLE 2-12 Formulation No. 84 85 86 87 88 89 90 Ingredients EPDM 75 7575 75 75 75 75 HNBR 1 25 25 25 25 25 25 25 Zinc oxide 10 10 10 10 10 1010 Antioxidant 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 Oil 1 10 10 1515 15 15 15 Oil 2 0 0 0 0 0 0 0 Peroxide 7 7 7 7 7 7 7 Zinc 40 50 10 2030 40 50 dimethacrylate Short nylon fibers 10 10 10 10 10 10 10 ShortTechnora 10 10 10 10 10 10 10 fibers Rubber Rubber hardness 54 62 32 3542 50 62 properties Gehman torsion T₅ −38.7 −38.5 −42.2 −41.6 −41.4−41.2 −40.6 (° C.) Amount of acetone 7.8 7.5 11.2 10.8 10.4 10.1 9.7extract (%) Permanent set (%) 53.1 60.0 34.2 41.1 48.1 55.0 61.9 CoggedCenter distance 2.5 3.5 3.4 V-belt variation (%) Transmitted torque (Nm)High-temp. durable life (hrs) Low-temp. durable ≧100 ≧100 ≧100 life(cycles) Hybrid Post-travel −0.23 −0.36 −0.34 V-belt interference (mm)Transmitted torque (Nm) High-temp. durable life (hrs) Low-temp. durable≧100 ≧100 ≧100 life (cycles) 

TABLE 2-13 Formulation No. 91 92 93 94 95 96 97 98 Ingredients EPDM 8080 80 80 80 80 80 80 HNBR 1 20 20 20 20 20 20 20 20 Zinc oxide 10 10 1010 10 10 10 10 Antioxidant 1 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 2020 Oil 1 0 0 0 0 0 0 0 0 Oil 2 0 0 0 0 0 5 5 5 Peroxide 7 7 7 7 7 7 7 7Zinc 10 20 30 40 50 10 20 30 dimethacrylate Short nylon fibers 10 10 1010 10 10 10 10 Short Technora 10 10 10 10 10 10 10 10 fibers RubberRubber hardness 35 41 48 56 69 34 37 42 properties Gehman torsion T₅−40.0 −39.4 −39.2 −39.1 −38.9 −43.2 −42.8 −42.5 (° C.) Amount of acetone3.1 3.1 3.0 3.0 3.0 6.0 5.8 5.6 extract (%) Permanent set (%) 28.5 35.442.4 49.3 56.2 30.4 37.3 44.3 Cogged Center distance 1.5 1.4 1.3 V-beltvariation (%) Transmitted torque 115 133 137 141 149 (Nm) High-temp. 9590 83 80 25 durable life (hrs) Low-temp. durable ≧100 ≧100 ≧100 life(cycles) Hybrid Post-travel −0.1 −0.09 −0.09 V-belt interference (mm)Transmitted torque 386 432 438 452 481 (Nm) High-temp. 302 293 271 25575 durable life (hrs) Low-temp. durable ≧100 ≧100 ≧100 life (cycles) 

TABLE 2-14 Formulation No. 99 100 101 102 103 104 105 Ingredients EPDM80 80 80 80 80 80 80 HNBR 1 20 20 20 20 20 20 20 Zinc oxide 10 10 10 1010 10 10 Antioxidant 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 Oil 1 0 00 0 0 0 0 Oil 2 5 5 10 10 10 10 10 Peroxide 7 7 7 7 7 7 7 Zinc 40 50 1020 30 40 50 dimethacrylate Short nylon fibers 10 10 10 10 10 10 10 ShortTechnora fibers 10 10 10 10 10 10 10 Rubber Rubber hardness 55 65 33 3743 48 63 properties Gehman torsion T₅ −42.3 −42.1 −46.3 −45.7 −45.5−45.4 −45.2 (° C.) Amount of acetone 5.5 5.3 8.7 8.4 8.1 7.8 7.5 extract(%) Permanent set (%) 51.2 58.1 32.3 39.2 46.2 53.1 60.0 Cogged Centerdistance V-belt variation (%) Transmitted torque (Nm) High-temp. durablelife (hrs) Low-temp. durable life (cycles) Hybrid Post-travel V-beltinterference (mm) Transmitted torque (Nm) High-temp. durable life (hrs)Low-temp. durable life (cycles) 

TABLE 2-15 Formulation No. 106 107 108 109 110 111 112 113 IngredientsEPDM 100 100 100 100 100 100 100 100 HNBR 1 0 0 0 0 0 0 0 0 Zinc oxide10 10 10 10 10 10 10 10 Antioxidant 1 1 1 1 1 1 1 1 Silica 20 20 20 2020 20 20 20 Oil 1 0 0 0 0 0 0 0 0 Oil 2 0 0 0 0 0 5 5 5 Peroxide 7 7 7 77 7 7 7 Zinc 10 20 30 40 50 10 20 30 dimethacrylate Short nylon fibers10 10 10 10 10 10 10 10 Short Technora 10 10 10 10 10 10 10 10 fibersRubber Rubber hardness 34 41 47 58 65 33 38 42 properties Gehman torsionT₅ −42.7 −42.2 −41.9 −41.7 −41.4 −45.8 −45.5 −45.3 (° C.) Amount ofacetone 3.1 3.1 3.0 3.0 3.0 6.0 5.8 5.6 extract (%) Permanent set (%)28.5 35.4 42.4 49.3 56.2 30.4 37.3 44.3 Cogged Center distance 1.6 1.61.4 V-belt variation (%) Transmitted torque 110 130 136 142 147 (Nm)High-temp. 93 90 86 79 33 durable life (hrs) Low-temp. durable ≧100 ≧100≧100 life (cycles) Hybrid Post-travel −0.11 −0.1 −0.1 V-beltinterference (mm) Transmitted torque 385 432 437 455 471 (Nm) High-temp.270 254 235 226 76 durable life (hrs) Low-temp. durable ≧100 ≧100 ≧100life (cycles) 

TABLE 2-16 Formulation No. 114 115 116 117 118 119 120 Ingredients EPDM100 100 100 100 100 100 100 HNBR 1 0 0 0 0 0 0 0 Zinc oxide 10 10 10 1010 10 10 Antioxidant 1 1 1 1 1 1 1 Silica 20 20 20 20 20 20 20 Oil 1 0 00 0 0 0 0 Oil 2 5 5 10 10 10 10 10 Peroxide 7 7 7 7 7 7 7 Zinc 40 50 1020 30 40 50 dimethacrylate Short nylon fibers 10 10 10 10 10 10 10 ShortTechnora 10 10 10 10 10 10 10 fibers Rubber Rubber hardness 54 64 33 3741 50 62 properties Gehman torsion T₅ −45.0 −44.5 −49.0 −48.7 −48.3−48.1 −47.7 (° C.) Amount of acetone 5.5 5.3 8.7 8.4 8.1 7.8 7.5 extract(%) Permanent set (%) 51.2 58.1 32.3 39.2 46.2 53.1 60.0 Cogged Centerdistance V-belt variation (%) Transmitted torque (Nm) High-temp. durablelife (hrs) Low-temp. durable ≧100 ≧100 life (cycles) Hybrid Post-travelV-belt interference (mm) Transmitted torque (Nm) High-temp. durable life(hrs) Low-temp. durable ≧100 ≧100 life (cycles)

Tables 2-1 and 2-2 (Formulation No. 1–15) show the data where the ratioof EPDM to hydrogenated acrylonitrile butadiene rubber HNBR 1 (Zetpol2010) is fixed at 25/75 and the amounts of oil and zinc dimethacrylateare changed. Likewise, Tables 2-3 and 2-4 (Formulation No. 16–30) showthe data where the ratio of EPDM to HNBR 1 is fixed at 35/65 and theamount of oil and the amount of zinc dimethacrylate are changed, Tables2-5 and 2-6 (Formulation No. 31–45) where the ratio of EPDM to HNBR 1 isfixed at 45/55 and the amount of oil and the amount of zincdimethacrylate are changed,. Tables 2-7 and 2-8 (Formulation No. 46–60)where the ratio of EPDM to HNBR 1 is fixed at 55/45 and the amount ofoil and the amount of zinc dimethacrylate are changed, Tables 2-9 and2-10 (Formulation No. 61–75) where the ratio of EPDM to HNBR 1 is fixedat 65/35 and the amount of oil and the amount of zinc dimethacrylate arechanged, Tables 2-11 and 2-12 (Formulation No. 76–90) where the ratio ofEPDM to HNBR 1 is fixed at 75/25 and the amount of oil and the amount ofzinc dimethacrylate are changed, Tables 2-13 and 2-14 (Formulation No.91–105) where the ratio of EPDM to HNBR 1 is fixed at 80/20 and theamount of oil and the amount of zinc dimethacrylate are changed, andTables 2-15 and 2-16 (Formulation No. 106–120) where the ratio of EPDMto HNBR 1 is fixed at 100/0 and the amount of oil and the amount of zincdimethacrylate are changed.

HNBR 1 shown in Tables 2-1 to 2-16 is hydrogenated acrylonitrilebutadiene rubber containing 36% bound acrylonitrile. On the other hand,Tables 3-1 and 3-2 show the data using hydrogenated acrylonitrilebutadiene rubber HNBR 2 (Zetpol 4110) containing 17% boundacrylonitrile. In Tables 3-1 and 3-2, the ratio of EPDM to HNBR 2 ischanged from 55/45 to 65/35 and then 75/25, and the amount of oil andthe amount of zinc dimethacrylate are changed for each rubber ratio.

TABLE 3-1 Formulation No. 121 122 123 124 125 Ingredients EPDM 55 55 5565 65 HNBR 2 45 45 45 35 35 Zinc oxide 10 10 10 10 10 Antioxidant 1 1 11 1 Silica 20 20 20 20 20 Oil 1 0 5 10 0 5 Oil 2 0 0 0 0 0 Peroxide 7 77 7 7 Zinc dimethacrylate 30 30 30 30 30 Short nylon fibers 10 10 10 1010 Short aramid fibers 10 10 10 10 10 Rubber Rubber hardness 46 43 41 4643 properties Gehman torsion T₅ (° C.) −36.0 −39.0 −42.3 −37.3 −40.3Amount of acetone extract (%) 3.0 5.6 8.1 3.0 5.6 Cogged Center distancevariation (%) 1.3 1.7 2.6 1.2 1.7 V-belt Transmitted torque (Nm) 137 137135 138 136 High-temp. durable life (hrs) 142 132 125 148 142 Low-temp.durable life (cycles) 75 ≧100 ≧100 ≧100 ≧100 High-temp. durable life:fine dispersion (hrs) 165 172 Hybrid Post-travel interference (mm) −0.09−0.15 −0.24 −0.09 −0.14 V-belt Transmitted torque (Nm) 440 435 430 441437 High-temp. durable life (hrs) 480 432 422 485 446 Low-temp. durablelife (cycles) 92 ≧100 ≧100 ≧100 ≧100 High-temp. durable life: finedispersion (hrs) 585 602 

TABLE 3-2 Formulation No. 126 127 128 129 Ingredients EPDM 65 75 75 75HNBR 2 35 25 25 25 Zinc oxide 10 10 10 10 Antioxidant 1 1 1 1 Silica 2020 20 20 Oil 1 10 0 0 0 Oil 2 0 0 5 10 Peroxide 7 7 7 7 Zincdimethacrylate 30 30 30 30 Short nylon fibers 10 10 10 10 Short aramidfibers 10 10 10 10 Rubber Rubber hardness 41 46 43 42 properties Gehmantorsion T₅ (° C.) −43.6 −38.7 −41.7 −44.8 Amount of acetone extract (%)8.1 3.0 5.6 8.1 Cogged Center distance variation (%) 2.5 1.2 1.8 2.7V-belt Transmitted torque (Nm) 135 137 135 134 High-temp. durable life(hrs) 138 145 138 131 Low-temp. durable life (cycles) ≧100 ≧100 ≧100≧100 High-temp. durable life: fine dispersion (hrs) 161 HybridPost-travel interference (mm) −0.26 −0.08 −0.16 −0.27 V-belt Transmittedtorque (Nm) 432 439 434 429 High-temp. durable life (hrs) 436 475 438431 Low-temp. durable life (cycles) ≧100 ≧100 ≧100 ≧100 High-temp.durable life: fine dispersion (hrs) 575

For the compounding of the rubber composition of formulations shown inTables 2-1 to 3-2, a Banbury mixer is used. More specifically, two typesof rubbers, EPDM and HNBR, and zinc dimethacrylate were concurrently putinto the mixer for mastication, and then an antioxidant, zinc oxide, afiller, oil, a crosslinker (peroxide) and short fibers were sequentiallyput into the mixer and mixed into a compound.

The resultant rubber compounds were evaluated for the later-describedrubber properties. Further, the typical rubber compounds in Tables 2-1to 3-2 were used to fabricate cogged V-belts and tension members forhybrid V-belts, and the resultant belts were evaluated in thelater-described manners.

In Tables 3-1 and 3-2, “High-temp. durable life: fine dispersion (hrs)”shows the data where a different compounding method from theabove-described was employed.

More specifically, zinc dimethacrylate powders were fine milled toseveral μm particles, and coarse particles of 20 μm or more wereclassified by an air classifier and removed. Next, HNBR was wrappedaround a roll mill with the surface temperature at 120° C., and the finemilled zinc dimethacrylate powders were added thereto by an amountcorresponding to each rubber formulation and mixed to preparehydrogenated acrylonitrile butadiene rubber dispersed with zincdimethacrylate.

The HNBR containing the zinc dimethacrylate and EPDM were put into aBanbury mixer for mastication, and then an antioxidant, zinc oxide, afiller, oil, a crosslinker (peroxide) and short fibers were sequentiallyput into the mixer and mixed into a compound.

<Measurements of Rubber Properties>

a) Measurement of Rubber Hardness

The mixed rubber compound was formed into a sheet of approximately 2.2mm thickness using a roll mill, and then press molded at 170° C. for 20minutes to prepare a crosslinked sheet of 2 mm thickness. Three plies ofthe rubber sheets were measured for rubber hardness by a durometer TypeD in conformity with JIS K6253.

b) Measurement of Gehman Torsion Level t₅

Each sample of the rubber compounds was measured for t₅ (the temperaturewhen its torsional stiffness has a value five times as large as that at23° C.) by a Gehman torsion tester in conformity with JIS K6261. At thattime, the sample was a 3 mm-wide strip in which the orientation of shortfibers was orthogonal to the length of the strip.

c) Measurement of Amount of Acetone Extract

The crosslinked rubber sheet was sliced to a thickness of 0.5 mm orless, and measured for the amount of acetone extract using a Type Iextractor in conformity with a JIS K6229 A method.

<Belt Evaluation>

a) High-Temperature Durability Test on Cogged V-belts

The resultant belt was subjected to a durability test in a two-axislayout. The diameters of the drive and driven pulleys were 128 mm and105 mm, respectively. An axial load (DW) of 120 kg (1176 N) was appliedto the driven pulley. The drive pulley was rotated at 6000 rpm with aload of 44 Nm applied to the driven pulley.

First, the belt was run for 24 hours with the atmospheric temperatureduring travel kept at 130° C., and removed from the tester. The removedbelt was measured for center distance to obtain a change in length.Specifically, the difference between the center distance before traveland that after 24 hours travel was divided by the center distance beforetravel to obtain a center distance variation on a percentage basis.

Then, the atmospheric temperature was decreased to 100° C., and therunning test was continued by continuing to run the belt until any cogcracked. The period of time during which the belt continued to travel at100° C. was defined as a high-temperature durable life.

In addition, belts using typical rubber formulations were measured forlateral surface temperature in travel 24 hours after the start of travelat 100° C. by an infrared non-contact temperature sensor.

b) Low-temperature Durability Test on Cogged V-belts

The resultant belt was subjected to a durability test in a two-axislayout. The diameters of the drive and driven pulleys were 68 mm and 158mm, respectively. An axial load (DW) of 120 kg (1176 N) was applied tothe driven pulley. The drive pulley was rotated at 1000 rpm with a loadof 44 Nm applied to the driven pulley. A cycle was repeated in which theatmospheric temperature was set at −30° C., the tester and belt werecooled at that temperature for an hour, and then the belt was run forfive minutes and cooled again for an hour. The low temperaturedurability of each belt was evaluated by how many cycles were repeateduntil any cog cracked.

c) Power Transmission Capability Test on Cogged V-belts

A power transmission capability test was conducted on each belt in atwo-axis layout. The diameters of the drive and driven pulleys were both105.8 mm. An axial load (DW) of 600 N was applied to the driven pulley.The drive pulley was rotated at 3000 rpm. The atmospheric temperaturewas set at 25° C. Transmitted torque was gradually increased. The beltpower transmission capability was evaluated by the transmitted torquewhen the belt percentage slip reached to 2%.

d) High-Temperature Durability Test on Hybrid V-belts

The resultant belt was subjected to a durability test in a two-axislayout. The diameters of the drive and driven pulleys were 126 mm and 71mm, respectively. An axial load (DW) of 1100 N was applied to the drivenpulley. The torque to the drive shaft was set at 63 Nm, and the drivepulley was rotated at 5300 rpm. The atmospheric temperature during belttravel was set at 110° C. First, the belt was run for 24 hours, thenremoved from the tester, and measured for permanent set in terms ofinterference (t2−t1).

Thereafter, the atmospheric temperature was decreased to 90° C., and therunning test was continued by continuing to run the belt until therubber layer of either one of the tension members cracked. The totalrunning time of the belt until it cracked was defined as ahigh-temperature durable life.

In addition, belts using typical rubber formulations were measured forlateral surface temperature in travel 50 hours after the start of travelat 90° C. by an infrared non-contact temperature sensor.

e) Low-Temperature Durability Test on Hybrid V-belts

The resultant belt was subjected to a durability test in a two-axislayout. The diameters of the drive and driven pulleys were 68 mm and 129mm, respectively. An axial load (DW) of 120 kg (1176 N) was applied tothe driven pulley. No torque is applied to the drive shaft, and thedrive pulley was rotated at 1000 rpm. A cycle was repeated in which theatmospheric temperature was set at −35° C., the tester and belt werecooled at that temperature for two hours, and then travel for fiveseconds and stop for ten seconds were repeated three times. The lowtemperature durability of each belt was evaluated by how many cycleswere repeated until the rubber layer of either one of the tensionmembers cracked.

f) Power Transmission Capability Test on Hybrid V-belts

A power transmission capability test was conducted on each belt in atwo-axis layout. The diameters of the drive and driven pulleys were both98.5 mm. An axial load (DW) of 3000 N was applied to the driven pulley.The drive pulley was rotated at 2500 rpm. The atmospheric temperaturewas set at 25° C. Transmitted torque was gradually increased. The beltpower transmission capability was evaluated by the transmitted torquewhen the belt percentage slip reached to 2%.

<Examination of Data in Tables 2-1 to 2-16>

With reference to the data shown in Tables 2-1 to 2-16, a graph isplotted between rubber hardness and transmitted torque which is theprincipal performance of each V-belt. FIG. 7 shows the relationships ofthe cogged V-belts, and FIG. 8 shows the relationships of the hybridV-belts.

Referring to FIGS. 7 and 8, in any of the cogged V-belts and hybridV-belts, the transmitted torque is abruptly decreased when the rubberhardness is decreased beyond 40. This shows that in order to transmitsufficient torque via any of the cogged and hybrid V-belts, the rubberhardness is preferably 40 or more.

With reference to the data shown in Tables 2-1 to 2-16, a graph isplotted between rubber hardness and high-temperature durable life. FIG.9 shows the relationships of the cogged V-belts, and FIG. 10 shows therelationships of the hybrid V-belts.

Referring to FIGS. 9 and 10, in any of the cogged V-belts and hybridV-belts, the high-temperature durable life is abruptly shortened whenthe rubber hardness exceeds 60. In other words, the belt becomes likelyto crack. Therefore, in order to enhance the power transmissioncapability, higher rubber hardness is more preferable. However, asclearly seen from FIGS. 9 and 10, excessively high rubber hardness willextremely deteriorate rubber cracking resistance and in turn extremelyshorten high-temperature durable life.

As can be seen from these points, the rubber material for heavy dutypower transmission V-belts preferably have a rubber hardness between 40and 60 when measured by a durometer Type D. Furthermore, it can be saidthat in order to obtain high-temperature durability while achieving highpower transmission capability, the rubber hardness preferably rangesfrom 45 to 58.

With reference to the data shown in Tables 2-1 to 2-16, a graph isplotted between Gehman torsion level t₅ and low-temperature durability.FIG. 11 shows the relationships of the cogged V-belts, and FIG. 12 showsthe relationships of the hybrid V-belts.

Referring to FIGS. 11 and 12, in any of the cogged V-belts and hybridV-belts, the low-temperature durability is considerably decreased whent₅ is increased beyond −35° C. Generally, cogged V-belts are required tohave a low-temperature durability of 50 cycles or more, and hybridV-belts are required to have a low-temperature durability of 60 cyclesor more. The figures show that in order to these requirements, theGehman torsion level t₅ is preferably between −50° C. and −35° C.Furthermore, it can be read from the figures that in order to provide avery excellent low-temperature durability of 100 cycles or more, any ofthe cogged and hybrid V-belts is required to have a Gehman torsion levelt₅ of −37° C. or less.

Rubber materials used for heavy duty power transmission V-belts arerequired to exhibit a small permanent set when undergoing heat andstress. The variation in the center distance of each cogged V-belt shownin Tables 2-1 to 2-16 can be considered to principally result from thatdeformation due to high lateral pressure from the pulley has been leftas a permanent set because the above high-temperature durability test isan accelerated evaluation carried out at high temperatures for a shortperiod of time. If the permanent set is large, this may cause beltbreakage in the vicinity of the cord or separation failure.

FIG. 13 is a graph plotted between the center distance variations andthe amounts of acetone extract of the cogged V-belts with reference tothe data shown in Tables 2-1 to 2-16. When the amount of acetone extractexceeds approximately 9%, the center distance variation due to permanentset becomes as large as 3% or more. In other words, in order to reducepermanent set of the belt due to lateral pressure, it is necessary toreduce the acetone extract of the rubber to about 9% or less. It can besaid that the acetone extract is preferably 7% or less, more preferably6% or less.

The permanent set of the tension member of a hybrid V-belt can beevaluated using the value of interference after the belt travel. If thepermanent set of the tension member is large and the interference thusbecomes small, the retention of blocks is deteriorated, leading to blockbreakage to shorten the belt life. Furthermore, noise during belt travelbecomes large, and the belt abnormally produces heat. Therefore, inorder to elongate the life of a hybrid V-belt, the interference of itstension member should be preserved.

FIG. 14 is a graph plotted between the post-travel interferences and theamounts of acetone extract of the hybrid V-belts with reference to thedata shown in Tables 2-1 to 2-16. FIG. 14 shows that in order to keepthe interference at −0.26 mm or more, the amount of acetone extract of arubber material needs to be 9% or less. It can be said from the figurethat the acetone extract is preferably 7% or less, more preferably 6% orless.

The principal constituents of a rubber composition extracted withacetone are oil, an antioxidant, and a polymer component of lowmolecular weight. It can be considered that when such organic substancesof low molecular weight not contributing to crosslinkage have a largecontent in the crosslinked rubber, the rubber material shortens itsrelaxation time and in turn easily causes a permanent set.

<Relation Between Rubber Properties and Amounts of CompoundingIngredients>

As described above, it can be said that in respect of rubber properties,the rubber hardness with a durometer Type D is preferably between 40 and60, t₅ by a Gehman torsion test is preferable between −50° C. and −35°C., and the acetone extract is preferably 9% or less. Exemplaryformulations satisfying such rubber properties are, in Tables 2-1 to2-16, Formulation Nos. 47–49, 62–64, 67–69, 77–79, 82–84, 92–94,107–109, 113 and 114.

First, consideration is given to the EPDM/HNBR ratio. As clearly seenfrom comparison of Formulation Nos. 47–49 with Formulation Nos. 2–4,17–19 and 32–34, the ratio of 55/45 or more (higher EPDM/HNBR ratio) candecrease the Gehman torsion level t₅ to low temperatures. However, as isobvious from comparison of Formulation Nos. 77–79 with Formulation Nos.92–94 and 107–109, the ratio over 75/25 shortens the high-temperaturedurable life (deteriorates the cracking resistance).

Therefore, it can be said that the EPDM/HNBR ratio preferably rangesfrom 55/45 to 75/25. Furthermore, since the results of Formulation Nos.62–64 on the Gehman torsion level t₅ and high-temperature durable lifeare excellent, the EPDM/HNBR ratio can be said to more preferably rangefrom 60/40 to 70/30.

Next, consideration is given to the amount of zinc dimethacrylate. FIG.15 is a graph plotted between the mixing ratio of zinc dimethacrylateand rubber hardness with reference to the results shown in Tables 2-1 to2-16. As is obvious from FIG. 15 and comparison of Formulation Nos.47–49 with Formulation No. 46, when the mixing ratio of zincdimethacrylate is low, the rubber hardness becomes excessively low andthe transmitted torque is thus insufficient. Furthermore, as is obviousfrom comparison of Formulation Nos. 47–49 with Formulation No. 50, whenthe mixing ratio of zinc dimethacrylate is high, the rubber hardnessbecomes high but the cracking resistance is deteriorated to adverselyaffect the high-temperature durability. These tendencies are also truefor Formulation Nos. 61–65 and 76–80.

Therefore, from these results, the mixing ratio of zinc dimethacrylatecan be said to preferably range from 20 to 40 parts by weight.Furthermore, since the results of Formulation Nos. 48, 63 and 78 on thetransmitted torque and high-temperature durable life are excellent, themixing ratio of zinc dimethacrylate can be said to more preferably rangefrom 25 to 35 parts by weight. Furthermore, FIG. 15 shows that in orderto set the rubber hardness between 40 and 60, the mixing ratio of zincdimethacrylate needs to range approximately from 20 to 40 parts byweight.

Next, consideration is given to the amount of acetone extract. Forexample, Formulation Nos. 53, 54, 58 and 59 have a large amount of oilunlike Formulation Nos. 48 and 49, and therefore their amounts ofacetone extract become large (10% or more). Additionally considering thecenter distance variations of the above cogged V-belts and thepost-travel interferences of the above hybrid V-belts, as the amount ofacetone extract is increased, the center distance variation becomeslarger and the post-travel interference becomes negatively larger. Thatis, the rubber permanent set becomes larger. This tendency is also truefor Formulation Nos. 62–64, 67–69, 73, 74, 77–79, 82–84, 88 and 89.

Therefore, from these results, the amount of acetone extract can be saidto be preferably 9% or less. Furthermore, since the results ofFormulation Nos. 62–64 and 77–79 on the center distance variation andpost-travel interference are excellent, the amount of acetone extractcan be said to be more preferably 6% or less.

FIG. 16 is a graph plotted between the amount of oil mixed and theamount of acetone extract with reference to the results shown in Tables2-1 to 2-16. It can be seen from the figure that the amount of oil mixedinto rubber needs to be approximately 10 parts by weight or less inorder to set the acetone extract at 9% or less, and approximately 5parts by weight or less in order to set the acetone extract at 6% orless.

Furthermore, as can be seen from FIGS. 13, 14 and 16, it is desirablethat the amount of oil mixed into a rubber composition is 5 parts byweight or less in order to further reduce the rubber permanent set.

The same results as in Tables 2-1 to 2-16 were also obtained when EPM ofTable 1 was used instead of the above EPDM and whenethylene-octene-copolymer of Table 1 was used instead. However, if theabove EPDM is replaced by the other grades of EPDM or the otherethylene-α-olefin elastomers in the exact same compounding ratio, therubber hardness has a slightly different value due to a difference inpolymer crystallinity. Therefore, in such a case, the rubber hardnessneeds to be controlled by changing the amount of carbon black or otherfillers.

Furthermore, in order to obtain a suitable cold resistance, it isdesirable that the ethylene-α-olefin elastomer (EPM, EPDM orethylene-octene-copolymer) is of amorphous grade as shown in Table 1.

The same effects could also be obtained when zinc diacrylate was usedinstead of zinc dimethacrylate. Therefore, it was found that anypolymerizable metal salt monomers of organic acids, typically such aszinc dimethacrylate and zinc diacrylate, were effectively used for thepresent invention.

<Examination of Data in Tables 3-1 and 3-2>

An example of effective means for obtaining sufficient cold resistanceeven at a mixing ratio of oil of 5 parts by weight or less (acetoneextract of 6% or less) is, instead of using HNBR (Zetpol 2010)containing 36% bound acrylonitrile shown in Tables 2-1 to 2-16, to useHNBR 2 (Zetpol 4110) containing 17% bound acrylonitrile shown in Tables3-1 and 3-2.

Tables 3-1 and 3-2 show examination results of formulation examples whenthe mixing ratio of zinc dimethacrylate is 30 parts by weight, themixing ratio of EPDM in 100 parts by weight of rubber component ischanged within the range of 55 to 75 parts by weight (i.e., the mixingratio of HNBR 2 is changed within the range of 45 to 25 parts byweight), and the mixing ratio of oil is changed within the range of 0 to10 parts by weight. The rubber properties of the formulation examplesare as follows: the rubber hardness measured with a durometer Type D isbetween 40 to 60, t₅ given by a Gehman torsion test is between −50° C.and −35° C., and the amount of acetone extract is 9% or less.

Gehman torsion level t₅ was compared between Formulation Nos. 121–129 inTables 3-1 and 3-2, having a EPDM/HNBR ratio of between 55/45 and 75/25and 30 parts by weight of zinc dimethacrylate, and Formulation Nos. 48,53, 59, 63, 68, 73, 78, 83 and 88 in Tables 2-7 to 2-11 having the sameEPDM/HNBR ratio and the same mixing ratio of zinc dimethacrylate.

When use is made of HNBR 1 containing 36% bound acrylonitrile (Zetpol2010) as shown in Formulation Examples of Tables 2-7 to 2-11, in orderto decrease the Gehman torsion level t₅ to a low temperature of −35° C.or less under the condition of 5 parts by weight or less of oil inrubber component, the EPDM/HNBR ratio needs to be increased to 65/35 andfurther 75/25. On the other hand, when use is made of HNBR 2 containing17% bound acrylonitrile (Zetpol 4110), equivalent Gehman torsion levelst₅ are achieved even when the mixing ratio of oil is about 10 parts byweight smaller than those of Formulation Examples of Tables 2-7 to 2-11.In other words, desired cold resistance can be provided in a wide rangeof the EPDM/HNBR ratio from 55/45 to 75/25, even at 0 to 5 parts byweight of oil in rubber component.

Therefore, in order to achieve both of more excellent cold resistanceand small permanent set of a belt, the bound acrylonitrile content inHNBR used can be said to be preferably 20% or less.

Furthermore, Tables 3-1 and 3-2 give to typical Formulation ExamplesNos. 121, 124 and 127 the results of the high-temperature durabilitytest, “High-temperature durable life: fine dispersion (hrs)”, using acompounding method in which the above-described zinc dimethacrylate isdispersed into HNBR and then the HNBR is blended with EPDM.

The formulation examples in which zinc dimethacrylate is fine dispersedinto HNBR clearly exhibited an elongated durable life over the othernormal formulation examples. This is probably because the finedispersion of zinc dimethacrylate into HNBR enhanced the crackingresistance of the rubber composition.

An example of rubber materials in which zinc dimethacrylate is finedispersed into HNBR is Zeoforte ZSC produced by Zeon Corporation.Zeoforte ZSC is prepared by using known methods to classify zinc oxideto remove coarse particles of 20 μm or more, add and mix the zinc oxideand a methacrylic acid into HNBR to react in situ, thereby producing ametal salt.

<Short Fibers>

Tables 4-1 and 4-2 show the results of measurement of hybrid and coggedV-belts on lateral surface temperature under high-temperature durabilitytest. These hybrid and cogged V-belts were fabricated from rubbercomposition formulations obtained by changing the amount of short fibersmixed into a peroxide-crosslinked rubber of a EPDM/HNBR 1 ratio of 65/35and a mixing ratio of zinc dimethacrylate of 30 parts by weight. In eachformulation, the amount of silica mixed thereinto was controlled to givea rubber hardness of 50.

TABLE 4-1 Temperatures of hybrid V-belts at self-heating depending uponthe types and amounts of short fibers Tensile Mixing ratio modulus(parts by weight) Short fiber type (length: 3 mm) (GPa) 3 5 10 20 25Short nylon fibers 5 140 136 135 133 133 Shortco-poly(paraphenylene-3,4′- 70 135 125 122 121 121oxydiphenylene-terephthalamide) fibers Shortpoly(paraphenylene-terephthalamide) 72 134 123 121 120 120 fibers Shortpoly(metaphenylene-isophthalamide) 17 138 127 124 122 122 fibers Shortpoly(paraphenylene-benzobisoxazole) 270 133 121 120 120 120 fibers Shortpolyvinyl alcohol fibers 26 137 126 123 122 122 Short holaromaticpolyester fibers 83 135 124 122 121 121 (unit: ° C.) 

TABLE 4-2 Temperatures of cogged V-belts at self-heating depending uponthe types and amounts of short fibers Tensile Mixing ratio modulus(parts by weight) Short fiber type (length: 3 mm) (GPa) 3 5 10 20 25Short nylon fibers 5 141 138 137 136 136 Shortco-poly(paraphenylene-3,4′- 70 138 128 125 124 124oxydiphenylene-terephthalamide) fibers Shortpoly(paraphenylene-terephthalamide) 72 135 125 124 122 122 fibers Shortpoly(metaphenylene-isophthalamide) 17 139 129 126 124 124 fibers Shortpoly(paraphenylene-benzobisoxazole) 270 135 125 123 121 121 fibers Shortpolyvinyl alcohol fibers 26 139 128 125 123 123 Short holaromaticpolyester fibers 83 137 127 125 123 122 (unit: ° C.)

As is obvious from Tables 4-1 and 4-2, when use is made of only shortnylon fibers with a tensile modulus of about 5 GPa, the matrix rubberneeds to have a higher elastic modulus in order to provide a rubberhardness capable of achieving a sufficient belt power transmissioncapability. In this case, the self-heating of rubber at the belt bendingbecomes considerably great. A great deal of rubber self-heating presentsproblems of induced rubber cracking due to heat aging and increasedrubber permanent set. It can be seen that also when the mixing ratio ofshort fibers is as small as 3 parts by weight, the matrix rubber needsto have a higher elastic modulus and therefore the rubber self-heatingbecomes great.

The results of Tables 4-1 and 4-2 show that in order to preserve beltpower transmission capability and suppress belt self-heating, the rubberneeds to contain 5 parts by weight or more of short organic fibers witha tensile modulus of 15 GPa to 300 GPa. Over 20 parts by weight of shortfibers decrease the effect of suppressing belt self-heating.Furthermore, this extremely deteriorates the processability of therubber composition, leading to the problems that a flat rubber sheetcannot be formed, the tackiness between rubber sheets is lost and itbecomes very difficult to mold a belt. Furthermore, the compounding costof the rubber composition becomes high. In consideration of thesepoints, the mixing ratio of short fibers preferably ranges from 5 to 20parts by weight.

1. A rubber composition for a heavy duty power transmission belt, therubber composition having a rubber hardness of 40 to 60 when measuredwith a durometer Type D, a value of t5 of −50° C. to −35° C. when givenby a Gehman torsion test, and an amount of acetone extract of 9% orless, wherein: (a) 20 to 40 parts by weight of a metal salt monomer ofan organic acid is mixed into 100 parts by weight of a rubber componentcomposed of an ethylene-α-olefin elastomer and hydrogenatedacrylonitrile butadiene rubber; (b) 5 to 35 parts by weight of shortfibers are mixed into 100 parts by weight of the rubber component; and(c) the amount of the ethylene-α-olefin elastomer in 100 parts by weightof the rubber component is 55 to 75 parts by weight.
 2. The rubbercomposition for a heavy duty power transmission belt of claim 1, whereinthe short fibers comprise organic short fibers with a tensile modulus of15 GPa to 300 GPa, and 5 to 20 parts by weight of the organic shortfibers are mixed into the rubber component.
 3. The rubber compositionfor a heavy duty power transmission belt of claim 2, wherein the organicshort fibers comprise at least one type of fibers selected from thegroup of poly(paraphenylene-terephthalamide) fibers,co-poly(paraphenylene-3,4′-oxydiphenylene-terephthalamide) fibers,poly-(metaphenylene-isophthalamide) fibers,poly(paraphenylene-benzobisoxazole) fibers, polyvinyl alcohol fibers,and holaromatic polyester fibers.
 4. A heavy duty power transmissioncogged V-belt wherein at least one of rubber elements constituting thebelt is formed from the rubber composition of claim
 1. 5. A heavy dutypower transmission V-belt comprising: a tension member formed of arubber layer having a cord embedded thereinto; and a plurality of blocksengaged at specified pitches and intervals in the lengthwise directionof the belt with the tension member, wherein the rubber layer is formedfrom the rubber composition of claim
 1. 6. The rubber composition for aheavy duty power transmission belt of claim 1, wherein theethylene-α-olefin elastomer is of amorphous grade, the boundacrylonitrile content in the hydrogenated acrylonitrile butadiene rubberis 20% or less, and the metal salt monomer of the organic acid is zincdimethacrylate or zinc diacrylate.
 7. The rubber composition of claim 1,wherein the mixing ratio of oil per 100 parts by weight of the rubbercomponent is less than 5 parts by weight.
 8. The rubber composition ofclaim 1, wherein the amount of acetone extract is 7% or less.
 9. Therubber composition of claim 8, wherein the amount of acetone extractranges from 3 to 7%.
 10. The rubber composition of claim 1, wherein theamount of acetone extract is 6% or less.
 11. The rubber composition ofclaim 10, wherein the amount of acetone extract ranges from 3 to 6%.